New test: Pureness hints

[jakearchibald]

This would be a tree-shaking test.

Something like:

main.js

import { bar } from './lib.js';
console.log(bar);

lib.js

function createDatabaseConnection() {
  console.log('connecting!');
  return {};
}

export const foo = createDatabaseConnection();
export const bar = 'bar';

Where the output wouldn't contain foo. The solution may require a pureness hint. WDYT @surma?

[jakearchibald]

Rollup solution, which uses a /*#__PURE__*/ hint.

[surma]

I make use of these pureness hints in rollup-plugin-assemblyscript to supply conveniences exports that can get tree-shookanized when unused:

const wasmUrl = /* injected by Rollup */;
const modulePromise = /*@__PURE__*/compileStreaming(fetch(wasmUrl));
const instancePromise = /*@__PURE__*/modulePromise.then(module => WebAssembly.instantiate(module, {}));

export {wasmUrl, modulePromise, instancePromise};

So I agree, this should be a subtest for treeshaking.

[AjayPoshak]

I am doing this.